Stimulated, in part, by the encouraging results with fast neutron therapy trials being conducted at the Hammersmith Hospital, interest in radiotherapy with high LET particles is presently increasing. Heavy particles, in addition to neutrons, which could be effective in radiotherapy include protons, helium ions, heavier ions, and negative pions. The project proposed herein is intended to provide comparative data describing the biological effects of several heavy charged particles (i.e., negative pions, helium ions, and one or two heavier ions). Measurements proposed are RBE and OER in bean roots and in cultured cells and RBE in the mouse foot. The growth rate of roots, survival rate vs depth for cultured cells, and both early and late reactions in the mouse foot will be observed. Results will be reported in a format useful to radiotherapists interested in the relative effectiveness of the particle studies under comparable physical conditions, in particular with similar widths for the Bragg peak.